As is known, many electrical or electronic appliances, such as for example television sets and radios, envisage a low-consumption operating mode, the so-called “standby” mode. In this mode, the electrical appliance is inactive with respective to the normal operating mode (for example, in the case of a television set, the mode whereby images are displayed), but can be turned on and off remotely, using a remote control. An electrical appliance in standby mode is in any case supplied by the electric grid (or battery) and consumes energy. The energy consumption is due to the presence of a microcontroller and of a sensor connected to the microcontroller, which are configured for receiving and processing commands supplied remotely via a remote control, and for this purpose are supplied.
FIG. 1 shows a portion of an electrical appliance 1, which comprises a supply circuit 4 designed to guarantee operation in standby mode of a microcontroller 5, to which it is connected, and of a sensor 6, connected to the microcontroller 5. The supply circuit 4 is a so-called “switch-mode power supply” (SMPS).
The electrical appliance 1 comprises a supply port 2, connected, for example, to the electric grid or to a battery (not illustrated), and receiving at an input a supply voltage VAL. The supply voltage VAL is then supplied at an input to the supply circuit 4, which supplies the microcontroller 5 both during the normal operating mode and during the standby operating mode. In particular, during the standby mode, the microcontroller 5 will be on and able to process any possible commands (for example, the command for switching on the electrical appliance 1) issued remotely using a remote control 7 and detected by the sensor 6. The electrical appliance 1 may further comprise a supply switch 8, arranged between the supply port 2 and the supply circuit 4, and configured so as to operate in conduction or in inhibition. The switch 8 may be, for example, a general switch of the electrical appliance 1. If the supply switch 8 operates in conduction, during the standby mode the supply circuit 4 and the microcontroller 5 are supplied. Instead, if the supply switch 8 operates in inhibition, the supply circuit 4 and the microcontroller 5 are not supplied, and the standby mode cannot be activated. In the latter case, the electrical appliance 1 is off and cannot be turned on remotely using the remote control 7.
Detailed examples of circuits that implement the supply circuit 4 are described in WO2010/106113. In particular, a supply circuit is described, which comprises a phototransistor and a MOSFET, which are connected in such a way that, in the presence of an electromagnetic signal incident on the phototransistor, the latter generates a photocurrent that biases the MOSFET in such a way as to drive it into conduction. Furthermore, the supply circuit is such that, when the MOSFET is in conduction, a transfer of electric power takes place from the supply port 2 to the microcontroller 5. In practice, the phototransistor and the MOSFET form an electro-optical relay.
In general, in the sector of applications of the so-called “zero-power standby” type, the photodetectors used within electro-optical relays need to withstand very high voltages, such as, for example, voltages higher than 400 V. Likewise, also the MOSFETs used in these applications should be able to sustain very high voltages. For this purpose, currently phototransistors and transistors of a discrete type are adopted, with consequent increase in the overall dimensions of the supply circuits.